When you copy and paste the same logic in many places, a single mistake must be fixed in every location. This leads to more work and a higher chance of missing a bug.

The Cost of Copying

This means having one official place for any piece of data or logic. If you need to change how something works, you only have to update it in that one spot.

Single Source of Truth

Instead of writing the same thing twice, you create a small, shared tool. This tool can then be used by different parts of the system whenever needed.

Creating Reusable Parts

Computers can understand complex instructions, but humans need to read and maintain the code. Simple designs are easier for other people to understand and fix.

Building for Humans

Over-engineering happens when you build complex solutions for simple problems. It is better to use the simplest tool that gets the job done effectively.

Avoiding Over-Engineering

Writing 'clever' or fancy code often makes it harder to read. If a design is too smart, it becomes difficult for anyone else to understand how it works later.

The Danger of Cleverness

This simple rule suggests that you should wait until you see the same pattern three times before trying to make it a reusable part. This prevents making things complicated too early.

The Rule of Three

Simple systems are easier to change because there are fewer moving parts to break. This allows the project to grow and adapt quickly over time.

Making Changes Faster

Complex tasks should be split into smaller, simpler steps. Each step should do one thing clearly without getting mixed up with other tasks.

Breaking Down Problems

Cognitive load is the amount of mental effort needed to understand something. Simple, non-repetitive designs keep this load low so people don't get overwhelmed.

Reducing Cognitive Load

Using the same simple approach everywhere makes the system predictable. When things are consistent, you can guess how one part works by looking at another.

Your Brain's Mental Budget